1. Field of the Invention
This invention relates to the acquisition and processing of images that display coloration artifacts precipitated by the use of flash illumination. More particularly it relates to a system and method for the image acquisition and processing of an image acquired with the use of a flash illumination source incorporated in a digital image capture device, such as a consumer oriented digital camera or mobile phone.
2. Discussion of Related Art
Coloration artifacts are sometimes displayed in images that have been acquired by the use of flash illumination. For example, in an image acquired by a small form factor digital camera or mobile phone, both equipped with built-in flash mechanisms, the conversion to red of the normally black pupils of a human subject's eyes, when the subject's face is illuminated by flash light, is a common occurrence. A similar coloration artifact, but usually of a color other than red, occurs when a pet subject's face, such as the face of a dog or a cat, is illuminated by a flash light. In the case of a dog, the black pupils of the subject's eyes are sometimes rendered as being yellow in color. In the case of a cat, the black pupils of the subject's eyes are sometimes rendered as being green in color. These particular coloration aberrations are a challenge to resolve because they are caused by the direct reflection of the flash light from the retinas of the subject's eyes.
Coloration artifacts such as those described above, can be reduced by diffusing the light emitted from the digital camera's built-in flash light source, and/or by redirecting the camera's flash light such that it indirectly illuminates the subject's face. However, these approaches require that the built-in illumination source be able to be moved relative to the axis of the camera's lens, be fitted with a light diffusing or redirecting elements, or both. This strategy is inconvenient, unreliable, and costly. Some digital cameras attempt to reduce the artifact by using multiple illumination source flashes. These flashes can close the irises of the subject's eyes, and reduce the light reflected back toward the camera from the subject's retinas, before the flash employed for the actual capture of the image is initiated. Again, this strategy is often not reliable. A third method uses image processing techniques for reducing the appearance of unwanted coloration artifacts. These locate the image color areas that correspond to predefined image area shape and color parameters, and modify the color of these areas so as to produce more acceptable image color characteristics. These techniques can be implemented within the camera taking the picture, or executed as a post process on a separate processing device. They have the downside of creating color corrected image areas that often do not look “real”. In other words, the color corrected pupils of the subject fail to display the subtle, detailed, reflections seen when directly viewing the eyes of a human or pet.
Thus there exists a need for an in-camera method and apparatus that can mitigate coloration artifacts precipitated by the use of flash illumination, that is reliable, low in cost, and produces captured images of superior quality.